Observational Cosmology

We're using observational astronomy to understand striking features of the cosmos, including the large-scale web of material in the Universe, supernovae, and the distorted appearance of distant galaxies.

Large scale structure

Large astronomical surveys measuring the positions of galaxies reveal a complicated large-scale structure within the observable Universe. Galaxies form where there are the highest concentrations of material in the Universe, so patterns of galaxies point to the physical properties of the early Universe. 

As we look to more and more distant galaxies, we see further into the history of the Universe, seeing galaxies at earlier and earlier times. By comparing the patterns of galaxies, we can uncover information about how much the Universe has grown.

Our research into the large scale structure proves that the expansion of the Universe is accelerating. From our research, we can obtain information on the exact form of this acceleration.

Within the University's Institute of Cosmology and Gravitation, our researchers are involved in astronomical survey projects that are advancing what we know about galaxies in the Universe, and helping to solve the mystery of dark energy.

Astronomical survey projects we're involved in

• Baryon Oscillation Spectroscopic Survey (BOSS)
• Dark Energy Survey (DES)
• The Extended Baryon Oscillation Spectroscopic Survey (eBOSS)
• Dark Energy Spectroscopic Instrument (DESI)
• VIMOS Public Extragalactic Redshift Survey (VIPERS)
• ESA Euclid mission

Gravitational lensing

It's often assumed that light travels in a straight line, but light can be bent by the effects of gravity in the Universe.

Wherever there is a clump of matter, there is a slight distortion of space and time – the light that passes is deflected. This bending of light is called ‘gravitational lensing.’ This leads to striking images of distant galaxies that appear to be stretched and magnified.

We research the appearance of these galaxies to understand the source of gravitational lensing, and to see what amounts of lensing can tell us about the behaviour of gravity itself. We expect the source of lensing to be the dark matter between us and the galaxies.

Transients

Astrophysical transients are phenomena that appear suddenly in the night sky, brighten for days to months and then fade away and disappear again. This includes novae (eruptions on the surfaces of white dwarfs), supernovae (the explosions of stars), tidal disruption events (stars ripped apart by black holes), and the still mysterious gamma-ray bursts and fast radio bursts. At the ICG, we specialise in the study of supernovae and tidal disruption events.

Supernovae

The violent explosions of stars, supernovae are some of the most energetic events in the Universe. At the ICG, we focus on three areas of supernova studies: progenitors, explosion physics, and cosmology. There are different types of supernovae and various types of stars; understanding which star ends up exploding as each type of supernova will advance our understanding of the life cycles of stars. Moreover, while we have a general idea of how different types of supernova explode (such as the internal collapse of massive stars or the thermonuclear explosion of white dwarfs), we still have to work out exactly how these explosions occur and understand the physics behind them. Finally, some types of supernovae can be used as cosmology probes. Type Ia supernovae have famously been used to measure distances to faraway galaxies and derive the expansion rate of the Universe. In the late 1990’s, this use of Type Ia supernovae led to the discovery that the expansion of the Universe was accelerating under the influence of a mysterious new phenomenon dubbed “dark energy.”

At the ICG, we are involved in several surveys that discover supernovae, study their properties, and use them in other experiments, such as cosmology and fundamental physics.

Tidal disruption events

Stars straying too close to the super-massive black holes at the centres of galaxies will be ripped apart by the strong gravitational fields of the black holes. Half of the star’s mass will be flung away while the rest will spiral into the black hole. On the way, the infalling matter will emit a bright flash of light – a tidal disruption flare – that lasts for weeks to months. First predicted in the 1980’s, less than 100 TDE candidates have been discovered to date. At the ICG, we work on discovering TDEs in spectroscopic galaxy surveys (DESI, 4MOST) and studying the properties of the host galaxies of these events. This is an exciting new field of study, with plenty of open questions to pick from.

Transients projects we're involved in

• Dark Energy Survey (DES)
• Dark Energy Spectroscopic Instrument (DESI)
• 4-metre Multi-Object Spectroscopic Telescope (4MOST)
• Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST)
• Hubble Space Telescope surveys (BUFFALO, SIRAH)

ICG staff currently researching transients

• Dr Or Graur
• Dr Daniel Whalen

Publication highlights

Discover our areas of expertise

Observational cosmology is one of the 4 areas of expertise within the Cosmology and Astrophysics research area – explore the others here.

Research groups

Interested in a PhD in Cosmology and Astrophysics?

Browse our postgraduate research degrees – including PhDs and MPhils – at our Cosmology and Astrophysics postgraduate research degrees page.